In prior art, a LED light bulb in place of an incandescent lamp typically is composed of one or more power type LED(s), a metal based PCB(MPCB), a heat sink with a series of dissipating fins, a driver including a switching power supply and a constant-current device, a connecting member, an anti-dazzle bulb shell and an electrical connector. Currently, a luminescent efficiency of such light bulb has caught up with that of widely used energy-saving fluorescent lamps. The luminescent efficiency of the entire energy-saving fluorescent lamps is 40-70 lm/W, but the luminescent efficiency of white LED element is already up to 130 lm/W. Therefore, the efficiency of the LED light bulb needs to be further improved. The main problems for the current LED light bulb lie in too high costs and sale prices, which are several times those of the energy-saving fluorescent lamps at the condition of same luminous flux, thereby being difficult to popularize. The factor resulting in high cost is not caused by the LED chip itself, but by the high cost aluminum alloy heat sink, the driver comprising a switching mode power supply having a transformer and a constant-current device as well as LED packaging. Such driver not only has a high cost, but also has a low efficiency. In addition, this driver further includes elements such as triode, transformer and electrolytic capacitor which have a short lifetime which is not matched with that of the LED. The average nominal lifetime of these elements is generally less than 25,000 hours, while the lifetime of LED itself should be up to 50,000-100,000 hours. That is, LED light bulb in the prior art for replacing the incandescent lamp has a relatively low luminescent efficiency of the entire light, too high cost, and not much long lifetime. If the LED light bulb is intended to replace the incandescent lamp and the energy-saving fluorescent lamp being widely used, and becomes main current of the general lighting, then the efficiency thereof should be further increased, the cost should be significantly decreased, the service lifetime should be elongated, and they should have the substantially same weight and volume as those of the incandescent lamp.
Light emitted from LED originates from PN junction of LED. The PN junction originally is a 4π illuminant. In the prior art, in order to concentrate light or connect with a metal heat sink, the PN junction of LED is arranged with a reflective layer, a reflective cup or a heat sink at one side thereof, that is, the original 4π illuminant is made as 2π or less than 2π illuminant. Thus, 2π light rays which are directed toward the heat sink, will outgo therefrom after single reflection, multiple reflections and various absorptions; while a part of 2π light rays which are directed toward a light outgoing surface, also will outgo after reflection, multiple reflections and various absorptions, since this part of 2π light will be directed toward the heat sink, thereby largely decreasing a light outgoing rate of the PN junction, i.e., the efficiency of the LED is decreased. Currently, an internal quantum efficiency of light emitted by the PN junction of the LED is already close to 90%, while external quantum efficiency thereof is only about 30%. The phrase of “the internal quantum efficiency being 90%” means that within the PN junctions, only 10% of injected electrons are drained without generating photon, while each of 90% of injected electrons generates a photon. However, one important reason for “the external quantum efficiency being only about 30%” is that the PN junction originally emitting 4π light becomes a 2π illuminator. If the PN junction of LED can be capable of emitting 4π light, it will certainly significantly enhance the luminescent efficiency of the LED.
With regard to this, researches have been previously carried out. For example, Chinese Patent No. 200510089384.X describes that a single LED chip is suspended in a light transmitting substance, so as to enable the chip to emit 4π light. However, this does not solve a problem of heat dissipation of the chip. This chip is suspended without a support plate and thus the power leads on the chip have a poor reliability. Thus, only a single small power chip can be used, and it is difficult to produce a reliable light having sufficient output light flux. And for example in United States (US) published patent application No. 2007/0139949, a plurality of small chips are in series installed on an expensive transparent thermal conducting substrate, such as sapphire, diamond, GaN, or an opaque thermal conducting substrate such as copper, SiC. Then the LED light bulb having a shape of the incandescent lamp is formed by connecting the above described substrate to a bulb head by thermal conducting lead wires and a bracket so as to dissipate heat, and providing a bulb shell at the outside thereof, which is not vacuum sealed, but filled with air therein and communicated with the ambient atmosphere. As described in the above US patent application, this the transparent thermal conducting substrate such as sapphire and diamond is very expensive and is difficult to be practical; and since the copper, SiC and the like are not transparent, it is impossible to achieve emitting 4π light. A path of dissipating heat for this kind bulb is chip→thermal conducting substrate→thermal conducting lead wire→thermal conducting bracket→bulb head. The path of dissipating heat ends the bulb head, resulting in a difficulty of making a thermal connection and a limited effect of dissipating heat. If the bulb head has the driver for the LED, then it will cause the path of dissipating heat to be disrupted and failed. At this condition, if the light bulb is vacuum sealed, then the path of dissipating heat will also be broken down. Therefore, it is difficult to produce a practical light having sufficient output luminous flux.
In the prior art, majority of the LED light bulbs employ power type LED having a low voltage and a high current. Each LED chip has one PN junction, its working current is as large as 0.35 A, even several amperes, and the electric power of 1 W to several Watts and above is concentrated on area of one to several square millimeters of the chip. Since the external quantum efficiency thereof is only about 30%, in addition to an energy difference between the injected electron and the photon generated by it as well as an energy difference between the photon generated by the PN junctions and the finally outgoing photon, about 70% of the electric power will be transformed into heat. How to dissipate so much heat is always a critical problem since this type of power LED first appears. LED is a semiconductor device, and a temperature rise of PN junctions thereof will cause the luminescent efficiency to be rapidly decreased, even the burning down of the PN junctions. To the present day, the heat dissipation is still one critical problem of this type of low voltage and high current power type LED lighting, including LED light bulbs.
In order to solve the problem of heat dissipation, the LED light bulb in the prior art mainly employs the metal passive heat sink having dissipating fins. The materials and shapes for this heat sink as well as how to increase the convective heat exchange with air have been studied and described in patents, for example, Chinese Patent No. 200510062323.4 and U.S. Pat. Nos. 6,787,999 and 7,144,135. This metal heat sink is typically made of aluminum alloy and has a bulky volume, a heavy weight and a high price. It is one of critical factors for high cost of the LED light bulb in the prior art.
Instead of the above described metal heat sink, the heat dissipation by means of liquid has also been studied, for example, Chinese Patent Nos. 200810093378.5, 200910100681.8, and 200910101643.4. The LED have been placed into a sealed bulb shell which is filled with thermal conducting liquid capable of transmitting light, which can be for example water, oil, glycol or other inert liquid. On one hand, the liquid has a much lower coefficient of thermal conductivity than that of the metal. As one example, the coefficient of thermal conductivity of water is about 0.7 W/(m·K), while the coefficient of thermal conductivity of the metal is 50-415 W/(m·K). The coefficient of thermal conductivity of the aluminum alloy which is commonly used in the heat sink of the LED light bulb, is 96-226 W/(m·K). It can be seen from the above that the liquid has a much lower thermal conductivity than that of the metal. On the other hand, since the coefficient of viscosity of the liquid is very large, for example, water having 8937 μP of viscosity, it is difficult for them to create convection. Concerning the above, the liquid has poor effects of thermal conduction and convection heat dissipation. Moreover, the use of liquid to dissipate heat also gives rise to the problems such as electroanalysis of the liquid, erosion of the liquid to the LED, the heat dissipation failure or even explosion caused by formation of a gas phase layer at a surface of LED likely due to the phase transition of the liquid, the liquid contamination caused after the breakage of the bulb shell, and the heavy weight. Thus, it is not easy to practically use and popularize it.
Use of gas for dissipating heat has already been studied, instead of the above described metal (solid) and liquid for heat dissipation. For example, the LED light bulb of Chinese Patent No. 201010176451.2 utilizes the nitrogen anion sealed in the bulb shell to dissipate heat. And for example, the LED light bulb of Chinese Patent No. 200910250434.6 utilizes a mixed gas of nitrogen and argon sealed in the bulb shell to dissipate heat. These methods are not practically used up to now. In addition to these LED light bulbs, other types of the lamps (such as cold cathode fluorescent lamps) may dissipate heat by applying high thermal conductivity of gas (such as He or a mixed gas of He with H2), for example as described in the Chinese Patent No. 200710148853.X. But it is difficult to create a limited convection, resulting in the limited effect of thermal conduction and dissipation, since the tube of the cold cathode fluorescent lamp has a large volume, which nearly occupies all the bulb shell. Therefore, it is not practically used today. And for example, metal halogen lamps also employ filling the bulb shell with the gas such as nitrogen and/or hydrogen, as can be seen from Chinese Patent No. 200580039670.3. The incandescent lamp also can be filled with the gas such as nitrogen and/or hydrogen. However, these lamps are different from the LED light.
Besides the above problem of heat dissipation, the LED light bulb in the prior art also has a driving problem of transforming the commercial high voltage power into the low voltage and high current. As described previously, the majority of the LED light bulbs in the prior art are power type LED operating at the condition of direct current, low voltage and high current. Their working voltages are in the range from several volts to tens of volts and their currents are in the range from 0.35 A to several Amperes. The current incandescent lamp and energy-saving fluorescent lamp for general lighting directly use the commercial alternating current with a voltage of 110-230V. Thus, if it is intended to directly replace them, then a driver including a AC/DC convertor will be necessary, so as to transform the alternating current with the high voltage into the direct current with the low voltage and a high current value. Such driver generally includes a switching power supply with elements such as triodes, transformers and electrolytic capacitors, and a constant current circuit. Since the volume of the LED light for replacing the incandescent lamp is not too large, the volume of the driver and the transformers should be kept as small as possible, while the difference between the input voltage and the output voltage is very large; this results in a low efficiency for electrical transformation, typically 70%-80%. This reduces the luminescent efficiency of the entire light. Meanwhile, because its efficiency is low, it generates a large amount of heat. Taking into consideration of the above generated heat by the driver and the heat generated by LED, the temperature of the driver will readily rise, thus this does not only further decrease the efficiency of the driver, but also will shorten lifetime of the driver. The elements such as triodes, transformers and electrolytic capacitors which are sensitive to temperature, are included in the driver. As temperature rises, their efficiency, lifetime and reliability will be significantly reduced. This renders the lifetime of the LED light bulb in the prior art to be not mainly dependent on LED, but on the driver. Moreover, the driver containing the switching power supply with the transformer and the constant current circuit has a complicated circuit and a high requirement on the elements, thus the cost thereof is high, which is another critical factor of leading to the high price of the prior art LED light bulb.
In order to replace such driver, a technology called as ACLED (alternating current LED) is being developed, as can be seen in for example Chinese Patent Nos. 200510020493.6 and 200610099185.1 and U.S. Pat. Nos. 7,515,248 and 7,535,028 as well as product AX3221 et al. A series of small current LED chips are connected in series in a way similar to a bridge rectifier circuit, installed on a MPCB, and provided with a heat sink. They can directly operate with the commercial alternating current and the driving circuit thereof is relatively simple. However, such LED currently has a relatively low efficiency, and it needs to tightly and thermally connect to a metal heat sink which has to be exposed in the air. Since ACLED is connected with a high voltage of alternating current, the metal heat sink will easily be charged and thus be unsafe. The prior art HVLED (high voltage LED), for example as described in Chinese Patent No. 201020159200.9, also has the same safety issues.
Furthermore, the LED is a kind of point light source, and about 100 lm of light will be concentrated on an area of about 1 mm2, thus an intensity of the light will be up to about tens of millions nits. If a person looks it in the eye directly, and will create a strong glare, thus leaving a shadow in the field of vision, then the eyesight will be heavily impacted within a short time. Therefore, the domestic lights should be provided with an antidazzle bulb shell or other devices for dispersing light. In order to obtain a good feel for the light, a light diffusing layer of the antidazzle bulb shell needs to have a sufficient thickness, while this will also reduce the transmission efficiency of the bulb shell. Typically, this will lose about 15% of light. This in turn reduces the luminescent efficiency of the entire light.
Concerning the above, if the prior art LED light is intended to widely replace the incandescent lamp and the energy-saving fluorescent light, for general lighting, then the LED light shall have a further improved luminescent efficiency, significantly reduced cost, an elongated life time, and volume and weight close to those of the incandescent lamp.